1. Field
The following description generally relates to a Light Emitting Diode (LED) driver apparatus and, for example, to an LED driver apparatus that is capable of sensing whether an LED array circuit is in an open state.
2. Description of Related Art
A Liquid Crystal Display (LCD) is thinner and lighter than many other types of display apparatuses. In addition, LCDs generally have lower driving voltage and consume less power than many other types of display apparatuses. Therefore, LCDs have been widely used. However, the liquid crystal panel of an LCD is a non-emitting device that does not emit light by itself. Thus, an LCD requires an additional backlight for supplying light to its liquid crystal panel.
A Cold Cathode Fluorescent Lamp (CCFL), a Light Emitting Diode (LED), and the like, are mainly used in a backlight unit (BLU) of an LCD. However, CCFLs utilize mercury; thus, CCFLs raise environmental concerns. In addition, CCFLs have slow response speed and low color representation. Thus, CCFLs are inappropriate for making an LCD that is light-weight, thin, short, or compact in size.
LEDs do not use a harmful material such as mercury; thus, they are environment-friendly in that sense. In addition, LEDs enable impulse driving. Also, a backlight unit comprising LEDs may exhibit high color representation. The amount of light from red (R), green (G), and blue (B) diodes of an LED backlight unit may be adjusted to freely change the luminance, color temperature, and the like of the emitted light. Accordingly, the luminance, color temperature and the like of an LCD using LEDs can be adjusted to a desired value, such as a predetermined value or a value that closely matches the image that is being reproduced. Thus, LEDs are appropriate for making an LCD that is light-weight, thin, short, and/or small. Therefore, LEDs have been widely used as a backlight source of an LCD and other display devices.
In an LCD backlight unit having LED arrays that each include a plurality of LEDs connected to one another, a driving circuit is often used to provide a constant current to each of the LED arrays, and a dimming circuit is often used to adjust the luminance, color temperature, and the like, to a desired value or to compensate for the color temperature and the like of the emitted light.
In such an LCD backlight unit, the circuits of LED arrays may frequently fail open with respect to a LED driver apparatus due to a physical impact to the device, an over-heating due to prolonged use, and the like, causing the backlight unit to malfunction or to deteriorate in performance. Accordingly, a protection circuit is desirable to sense whether any of the circuits of LED arrays has failed open.
However, based on an abnormal forward voltage generated either at an initial driving or by a peak current of a constant current, a conventional protection circuit may determine that the circuits of LED arrays are open, when the circuits are actually not in an open state.
For example, if the LED arrays are initially turned on, a forward voltage of the LED array may suddenly increase, causing a large increase in voltage. The large differences in the magnitude of voltages are frequently used to determine whether an LED array circuit is in an open state. For instance, a conventional protection circuit may determine a large voltage difference between the forward voltages Vf of the LED arrays to detect an LED array that has failed open. In determining that one LED array has failed open, the backlight unit may generate a driving voltage by excluding the LED array having the large voltage difference. As a result, the LED array having the large voltage difference may no longer operate in a normal manner.
In addition, the forward voltage of the LED array is frequently temporarily lowered to a value close to 0V due to a peak current of a constant current source. The conventional protection circuit may detect this change as indicating that the circuit of an LED array has failed open. In such an event, a driving voltage is generated by excluding the forward voltage of the corresponding LED array that is determined to be in an open state, preventing the corresponding LED array from operating in a normal manner.